Activation of the molecular oxygen present in air is a very important process for living organisms. It enables a very wide range of oxidation reactions to be carried out using oxygen as an oxidizing agent, despite its very high stability. Nature often, but not exclusively, uses metal ions such as iron or copper to achieve this activation. This lecture presents various metallo-enzymatic polynuclear systems that catalyze surprising oxidation reactions. The first is the transformation of a tyrosine into a tyrosinyl radical in ribonucleotide reductases (RNRs). This reaction is of major importance, since it is this tyrosinyl radical that enables RNRs to synthesize deoxyribonucleotides, the precursors of DNA. In reality, RNRs are found in nature using either two iron atoms or two manganese atoms, and functioning mechanistically differently. The mechanisms of oxygen activation by these two systems are presented. Very recently, an RNR using one iron and one manganese atom has been discovered.
A second fascinating reaction is presented to illustrate the intervention of complex clusters in oxidation reactions. This is the oxidation of methane by oxygen to methanol, catalyzed by methane monooxygenase (MMO). MMO possesses multiple copper atoms absolutely essential for activity within a polynuclear assembly whose structure has yet to be determined.
